This invention relates to a process for the production of semi-conducting silicon layers on oxidized aluminum films by means of an isothermal silicon separation from silicon-aluminum-zinc melts.
Various processes are known for the production of thin crystalline silicon layers on foreign substrates. A number of process systems may be characterized in that by evaporation of solid silicon under vacuum by means of resistance heating or by electron bombardment silicon atoms are condensed on a substrate; this also includes the condensation of charged silicon atoms. In particular those process systems are of technical importance which may be characterized by a reactive condensation of silicon atoms on foreign substrates, such as for instance the reduction of halide or hydrohalide compounds with siicon, e.g. SiCl.sub.4 or SiHCl.sub.3. As compared with a simple condensation, the reactive condensation is distinguished by higher separation rates. Sometimes the required high substrate temperature is of a disadvantage for the reactive condensation, which temperature can very greatly limit the choice of suitable substrates. Both for the simple and the reactive condensation the high energy requirements are of a disadvantage, related to the separated quantity of silicon. As compared therewith, process systems based on the separation of silicon from solution melts have the advantages of a high separation rate at a low process temperature and a comparatively lower energy requirement per separated silicon quantity. Next to the above-mentioned factors which in particular determine the economies of a production process, for the technical application of thin silicon layers the achievable physical parameters have an importance of the same rank, however, such as for instance the doping, the life achievable of the minority charge carriers and the properties of the crystallinity. With the process systems mentioned on amorphous foreign substrates only polycrystalline silicon layers are able to be produced; the charge carrier transport actions in silicon layers having a high crystalite density are sometimes so badly affected that a technical use for semi-conductor elements must be precluded. For specific technical uses it is therefore of material importance that silicon layers are able to be produced which possess a coherent crystal structure across extended areas, the lateral dimensions of the crystallits preferably having to be significantly larger than the thickness of the silicon layer.